An apparatus and method for automatically generating and adjusting fuzzy reasoning, i.e. logic, rules based on changes in the reasoning error. The apparatus includes a fuzzy reasoning section that performs fuzzy logic based on the fuzzy reasoning rules stored in the a rule memory. The parameters of the fuzzy reasoning rules are adjusted in a parameter tuning section based on the output of the fuzzy reasoning section and predetermined input and output data. A reasoning error calculation section calculates a reasoning error and a change in the reasoning error based on the results from the fuzzy reasoning section and the predetermined input and output data. The reasoning error calculation section also disables the parameter tuning section when the calculated reasoning error is less than a predetermined first threshold value. When the calculated reasoning error is greater than or equal to the predetermined threshold value and the change in the reasoning error is less than a predetermined second threshold value, a rule generation section generates one or more fuzzy reasoning rules and regenerates the fuzzy reasoning rules stored in the rule memory based on the new fuzzy reasoning rule(s) so that optimal fuzzy reasoning rules are obtained.